Viral vector for the targeted transfer of genes in the brain and spinal cord

ABSTRACT

The invention relates to novel peptides, polypeptides or proteins which specifically bind to cells of the brain and/or the spinal cord. The peptides, polypeptides or proteins can be part of a viral capsid, and they can be used for guiding a recombinant viral vector selectively to the brain and/or spinal cord after systemic administration to a subject, where it provides for a tissue-specific expression of one or more transgenes. The invention therefore also relates to a recombinant viral vector, preferably an AAV vector, comprising a capsid containing at least one of the peptides, polypeptides or proteins of the invention and at least one transgene which is packaged within the capsid. The viral vector is particularly suitable for the therapeutic treatment of a disease or functional disorder of the brain and/or the spinal cord. The invention further relates to cells and pharmaceutical compositions comprising the viral vector of the invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 16/263,529, filed Jan. 31, 2019, which is a divisional of U.S. Ser. No. 15/303,950, filed Oct. 13, 2016, which is the U.S. National Stage of International Patent Application No. PCT/EP2015/058123, filed Apr. 15, 2015, each of which is hereby incorporated by reference in its entirety, and which claim priority to German Patent Application No. 102014207498.3, filed Apr. 17, 2014.

SEQUENCE LISTING

The sequences listed in the accompanying Sequence Listing are presented in accordance with 37 C.F.R. 1.822. The Sequence Listing is submitted as an ASCII computer readable text file, dated Jun. 30, 2020, 41 kb, which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

The gene therapeutic treatment by use of viral vectors is a promising treatment option for diseases that do not respond or do not sufficiently respond to conventional treatment. This approach is based on the introduction of therapeutic genes into the organism to be treated using viruses which have been modified to include the sequence of the respective gene in their genome. Viral vectors which have been used for gene therapy in gene therapeutic approaches are based on retroviruses, lentiviruses, adenoviruses and adeno-associated viruses.

Adeno-associated viruses (AAV) are promising candidates for use in clinical practice because they are considered as relatively safe. AAV vectors are capable of introducing a transgene into a tissue and expressing same stably and efficiently. At the same time, these vectors do not possess any known pathogenic mechanism [1]. The AAV vectors of serotype 2 (AAV2) are of particular importance for clinical use, and these vectors have been examined particularly well. After introduction by AAV vectors, the transgenes can be present within the transfected cell in different forms, for example as episomal, single-stranded or double-stranded DNA. Concatemeric forms of DNA were also found in transduced cells.

The genome of AAV2 is a linear, single-stranded DNA molecule of approximately 4700 nucleotides in length, and it comprises inverted terminal repeats (ITRs) at both ends. The genome further comprises two large open reading frames which are referred to as replication region (rep) and capsid region (cap). The replication region encodes proteins which are required in connection with virus replication. In contrast, the capsid region encodes the structural proteins VP1, VP2 and VP3 which make up the icosahedral capsid of the virus.

As most of the vectors which can be used in gene therapy and which are known in the state of the art, wild-type AAV vectors, e.g. the disclosed AAV2 vectors, do not possess sufficient specificity for a specific tissue but instead infect a wide variety of cell types. Upon systemic administration of these wild-type vectors, the target tissue is insufficiently transduced, and severe immune reactions have to be expected in the treated patient due to the undesired transduction of other tissues. Progress has been made with the development of viral vectors having an increased specificity for particular organs by using peptide ligands that are capable of guiding the vectors to specific organs [2-3]. It could be shown that specific peptide ligands provide for a “homing” to different organs such as the brain.

Reference [4] describes a method that allows for the screening of capsids of AAV 2 with modified tropism in randomized peptide libraries. From these libraries, vectors can be isolated that specifically transduce a desired cell type in vitro. However, it has been found that capsids selected in this way are often unsuitable for being used in vivo since the required specificity is missing in an animal model [5].

From the clinical perspective, the brain is an extremely relevant organ, since it is the starting point of a variety of neurological diseases. Considerable efforts have been made to make this organ accessible for gene therapeutic interventions [6-12]. However, the blood brain barrier, which is composed of endothelial cells, pericytes and astrocytes and which seals the brain off from circulating particles, toxins and signal compounds, represents a barrier that cannot be passed by normal vector systems. Since suitable vector systems that transduce the brain with sufficient efficiency after intravenous application are not available so far, present gene therapy vectors are normally injected directly into the brain [13] which is associated with a higher risk for the patient. The possibility of making the blood brain barrier permeable for a short time, e.g. by ultrasound [14] or by chemical agents [7] is also regarded as very risky. Accordingly, there is a high demand for agents, which are capable of modulating the tropism of viral vectors, thereby providing for a sufficient cell or tissue specificity which renders possible a targeted transport of a viral vector to tissues of the brain or spinal cord. Such vectors can provide for the specific expression of therapeutic genes in these tissues, thereby effectively treating diseases and/or functional conditions of the brain and the spinal cord.

The present invention provides viral vectors for the targeted gene transfer into the brain and spinal cord. The viral vectors of the present invention express on their capsid surface so far unknown amino acid sequences that are specifically recognized in vivo by receptors on the neurons of the brain and the endothelial cells of the blood vessels of the brain and spinal cord. In this way, the viral vectors of the present invention, after systemic administration to a subject, specifically transduce the tissues in the brain and spinal cord.

The viral vectors of the present invention further enable a strong and long persisting expression of a transgene in the neurons of the brain and in the endothelial cells of the blood vessels of the brain and spinal cord. Therefore, the vectors are particularly suitable for the gene therapeutic treatment of defined diseases or conditions of the brain and spinal cord. It has been furthermore found that the AAV vectors produce only a slight immune reaction after transfection in the host, and they are therefore particularly suitable for gene therapy.

DESCRIPTION OF THE INVENTION

In the present invention, various sequences that are specific for the central nervous system, i.e. for the brain and spinal cord, were identified by selection in a randomized AAV2 heptamer peptide library. A heptamer having particular specificity for the brain was peptide NRGTEWD (SEQ ID NO:1). Based on this sequence, the recombinant viral vector rAAV2-NRGTEWD (SEQ ID NO:1) was produced which expresses the peptide sequence NRGTEWD (SEQ ID NO:1) as a partial sequence of the capsid protein VP1. Subsequently, vector rAAV2-NRGTEWD (SEQ ID NO:1) was administered intravenously to mice and a clear specificity of the vector for the central nervous system could be observed both in vitro and in vivo. Both neurons of the brain and endothelial cells of the blood vessels of the brain and the spinal cords were transfected by the vector. The specificity was confirmed by staining with CD31 as described in the present examples.

A further group of peptides, which also showed specificity for the brain and spinal cord, encompassed peptides ADGVQWT (SEQ ID NO:2), DDGVSWK (SEQ ID NO:3), SDGLTWS (SEQ ID NO:4) and SDGLAWV (SEQ ID NO:5). These peptides contained the general motif XDGXXWX (SEQ ID NO: 6).

The present invention therefore provides different peptide sequences which are specific for the brain and spinal cord and which are particularly suitable for guiding therapeutic agents, such as viral vectors, to the brain or spinal cord of a subject to be treated, respectively.

In a first aspect, the present invention therefore relates to a peptide, polypeptide or protein which specifically binds to cells of the brain and/or spinal cord, wherein the peptide, polypeptide or protein comprises the amino acid sequence of SEQ ID NO:1 or a variant thereof, wherein the variant differs from the amino acid sequence of SEQ ID NO:1 by modification of a maximum of one amino acid. The peptide, polypeptide or protein of the present invention preferably binds to endothelial cells and/or neurons of the brain or spinal cord.

In a second aspect, the present invention relates to a peptide, polypeptide or protein, which specifically binds to cells of the brain and/or spinal cord, wherein the peptide, polypeptide or protein comprises the general amino acid sequence of SEQ ID NO:6. In a particularly preferred embodiment, the peptide, polypeptide or protein comprises one of the sequences of ADGVQWT (SEQ ID NO:2), DDGVSWK (SEQ ID NO:3), SDGLTWS (SEQ ID NO:4) or SDGLAWV (SEQ ID NO:5) or a variant thereof, wherein the variant differs from the respective amino acid sequence of SEQ ID NO:2-5 by modification of a maximum of one amino acid. The peptide, polypeptide or protein of the present invention preferably binds to endothelial cells and/or neurons of the brain or spinal cord.

In the context of the present disclosure, the term “peptide” refers to a linkage of 2-10 amino acids which are connected to each other by a peptide bond. The term “polypeptide” refers to a linkage of 11-100 amino acids that are connected to each other by a peptide bond. Polypeptides with more than 100 amino acids are referred to herein as a “protein.”

In a particularly preferred embodiment according to the invention, the peptide sequence of SEQ ID NO:1 or a variant thereof or SEQ ID NO:2-6 or a variant thereof, which are specific for the brain and spinal cord, is a part of a capsid protein of a virus. This means that the sequence, which is specific for the brain and spinal cord, is present as part of a capsid protein of the virus. To produce such capsid proteins, a corresponding nucleotide sequence which codes for the peptide is cloned into the region of the virus genome which codes for a capsid protein of the virus. If the sequence, which is specific for the brain and the spinal cord, respectively, is expressed as part of a capsid protein, it can be presented in many copies across the surface of the viral vector.

The capsid protein is preferably one which is derived from an adeno-associated virus (AAV). The AAV can be any of the serotypes described in the prior art, wherein the capsid protein is preferably derived from an AAV of one of the serotypes 2, 4, 6, 8 and 9. A capsid protein of an AAV of serotype 2 is particularly preferred.

The capsid of the AAV wild-type is made up of the capsid proteins VP1, VP2 and VP3, which are encoded by the overlapping cap region. All three proteins have the same C-terminal region. The capsid of AAV comprises about 60 copies of the proteins VP1, VP2 and VP3, expressed in a ratio of 1:1:8. If a nucleotide sequence coding for one of the peptides, which is specific for the brain and the spinal cord, respectively, and which is described herein is cloned at the C-terminus into the reading frame of VP1 (i.e., in the region that is identical in all three proteins), it can be expected that theoretically 60 of the specific peptides can be found on the capsid surface.

If an AAV vector in the context of the present invention is modified, the nucleotide sequence coding for the peptide which is specific for the brain is then cloned into the cap region at the 3′ end of the genome. The sequence encoding the peptide being specific for the brain and spinal cord, respectively, can be cloned into the genomic sequence of one of the capsid proteins VP1, VP2 or VP3. The capsid proteins of AAV2 are illustrated by way of example in SEQ ID NO:7 (VP1), SEQ ID NO:8 (VP2), and SEQ ID NO:9 (VP3).

In one particularly preferred embodiment according to the invention, the sequence encoding the peptide, which is specific for the brain and spinal cord, respectively, is cloned into the reading frame of a VP1 gene, preferably in the VP1 gene of AAV2 shown in SEQ ID NO:7. It should be noted in this case that the insertion of the cloned sequence does not lead to any change of the reading frame, nor to a premature termination of translation. The methods required for the above will be readily apparent to a person skilled in the art.

In all three capsid proteins of AVV, sites have been identified at which peptide sequences can be inserted for the homing function [15-20]. Among other things, the arginine which occurs in the VP1 of AAV2 at position 588 (R588) has specifically been proposed for the insertion of a peptide ligand [21-22]. This amino acid position of the viral capsid is apparently involved in the binding of AAV2 to its natural receptor. It has been suggested that R588 is one of four arginine residues which mediates the binding of AAV2 to its natural receptor [23-24]. A modification in this region of the capsid weakens the natural tropism of AAV2, or eliminates it completely.

Accordingly, it is particularly preferred according to the invention that the peptide sequence of SEQ ID NO:1 or a variant thereof or of SEQ ID NO:2-6 or a variant thereof is present in inserted form in the region of the amino acids 550-600 of the VP1 protein of AAV2, in particular of the VP1 protein of SEQ ID NO:7.

Even more preferably, the peptide sequence is present in inserted form in the region of amino acids 560-600, 570-600, 560-590, 570-590 of the VP1 protein.

Thus, the peptide sequence of SEQ ID NO:1 or a variant thereof or SEQ ID NO:2-6 or a variant thereof can adjoin, by way of example, directly behind one of the following amino acids of the VP1 protein, particularly the protein of SEQ ID NO:7: 550, 551, 552, 553, 554, 555, 556, 557, 558, 559, 560, 561, 562, 563, 564, 565, 566, 567, 568, 569, 570, 571, 572, 573, 574, 575, 576, 577, 578, 579, 580, 581, 582, 583, 584, 585, 586, 587, 588, 589, 590, 591, 592, 593, 594, 595, 596, 597, 598, 599 or 600.

It is particularly preferred that the amino acid sequence of SEQ ID NO:1 or a variant thereof or SEQ ID NO:2-6 or a variant thereof follows the amino acid 588 of the VP1 protein of SEQ ID NO:7, as shown in the examples. It is possible in this case that one or more, and particularly up to 5 (i.e., 1, 2, 3, 4 or 5) amino acids which are the result of the cloning are situated between the arginine residue at position 588 and the first amino acid of the peptide of the invention or the variant thereof. Likewise, one or more, and particularly up to 5 (i.e., 1, 2, 3, 4, or 5) amino acids can be situated behind the last amino acid of the peptide of the invention or the variant thereof.

The sites and regions in the amino acid sequence of the capsid protein indicated above for VP1 apply analogously to the capsid proteins VP2 and VP3 of AAV2. Because the three capsid proteins VP1, VP2 and VP3 of AAV2 differ only by the length of the N-terminal sequence and accordingly have an identical C-terminus, a person skilled in the art will have no problem making a sequence comparison to identify the sites indicated above, for the insertion of the peptide ligands, in the amino acid sequences of VP1 and VP2. As such, the amino acid 588 in VP1 corresponds to position R451 of VP2 (SEQ ID NO:8) and position R386 of VP3 (SEQ ID NO:9), respectively.

SEQ ID NO:10 shows an example of the sequence of the VP1 protein of AAV2 after introduction of the peptide sequence of SEQ ID NO:1. Due to the cloning, the capsid protein has two additional amino acids which do not occur in the native sequence of the VP1 protein of AAV2. As such, the peptide sequence of SEQ ID NO:1 is flanked at its N-terminus by a glycine in position 589, and at its C-terminus by an alanine in position 597. In addition, the asparagine at position 587 of the native sequence is replaced with a glutamine.

In one particular embodiment, the present invention therefore also relates to a capsid protein which comprises or consists of:

(a) the amino acid sequence of SEQ ID NO:10; (b) an amino acid sequence which is at least 80%, and preferably 90, 95 or 99%, identical to the amino acid sequence of SEQ ID NO:10 and furthermore (i) comprises the amino acid sequence of SEQ ID NO:1 or (ii) an amino acid sequence, which differs from the amino acid sequence of SEQ ID NO:1 by modification of one amino acid; or (c) a fragment of one of the amino acid sequences defined in (a) or (b).

In a further aspect, the invention is directed to a viral capsid, which comprises a peptide, polypeptide or protein which specifically binds to cells of the brain or spinal cord, respectively, and comprises the amino acid sequence of SEQ ID NO:1 or a variant thereof or SEQ ID NO:2-6 or a variant thereof.

Furthermore, the present invention also provides a nucleic acid encoding a peptide, polypeptide or protein as described above. A nucleic acid which encodes a capsid protein which comprises a peptide, polypeptide or protein according to the invention as described above, is likewise provided. Preferably, the nucleic acid coding for the capsid protein comprises the nucleotide sequence of SEQ ID NO:11 or a nucleotide sequence derived from the same with at least 80% sequence identity. A plasmid comprising such a nucleic acid is also provided.

In yet another aspect, the invention relates to a recombinant—i.e., produced by means of genetic engineering techniques—viral vector, having a capsid and at least one transgene packaged therein, wherein the capsid comprises at least one capsid protein having the amino acid sequence of SEQ ID NO:1 or a variant thereof or SEQ ID NO:2-6 or a variant thereof. The recombinant viral vector can be a recombinant AAV vector—for example, of serotype 2, 4, 6, 8, 9. AAV vectors of serotype 2 are particularly preferred.

The different AAV serotypes differ mainly by their natural tropism. As such, wild-type AAV2 binds more readily to alveolar cells, while AAV5, AAV6 and AAV9 mainly infect epithelial cells. A person skilled in the art can take advantage of these natural differences in the specificity of the cells to further enhance the specificity mediated by the peptides according to the invention for certain cells or tissues. At the nucleic acid level, the various AAV serotypes are highly homologous. For example, serotypes AAV1, AAV2, AAV3 and AAV6 are 82% identical on the nucleic acid level [25].

The capsid of the viral vectors according to the invention comprises one or more transgenes. A gene which has been introduced by genetic engineering into the genome of the vector is termed a transgene. The transgene (or transgenes) can be DNA or RNA. Preferably, it is single-stranded DNA (ssDNA) or double-stranded DNA (dsDNA), such as genomic DNA or cDNA. Preferably, the transgene which is to be transported with the aid of the recombinant viral vector according to the invention is a human gene. Suitable transgenes include, for example, therapeutic genes to replace a dysfunctional gene in patients. They can also be genes which are not expressed in the corresponding target tissue, or are only expressed to an insufficient extent. In one preferred embodiment, the transgene which is expressed from the viral vector according to the invention is a.

The vectors of the present invention can be used, amongst others, for the treatment of Multiple Sclerosis (MS). In this case, the transgene can be, e.g. a gene which encodes a membrane protein or a tight junction protein, such as for claudin and occludin. Preferably the transgene is a gene from the family of claudins, e.g. the gene encoding claudin 1. The overexpression of one of such genes could be helpful for “sealing” the blood brain barrier that is damaged by the disease.

In addition, a gene can be used for the treatment of MS which encodes a chemokine antagonist. For example, a negative-dominant mutant of the chemokine CCL2 (aka MCPJ) can be expressed which is referred to as “CCL2-7ND”. CCL2 provides for the attraction of immune cells to the site of inflammation which in the case of MS results in the inflammatory degradation of the myelin sheaths of neurons. In contrast, the dominant-negative variant “CCL2-7ND” forms dimers and blocks the receptor CCL2, thereby interfering with the signal cascade such that the immune cells are no longer attracted by the neurons.

For the treatment of Alzheimer's Disease, e.g. the gene encoding neuraminidase 1 (NEU1), neprilysine or cholesterol 24 hydroxylase can be overexpressed which leads to the degradation of amyloid 13, plaques and therefore can contribute to an amelioration of the state of disease.

Parkinson's disease can be treated by vector-mediated overexpression of e.g. the neurotrophic factors of glia cells (GDNF), the aromatic L-amino acid decarboxylase, the tyrosine hydroxylase or the GTP cyclohydrolase 1, wherein a positive influence on the dopaminergic system can be expected. A treatment of the spinal muscle atrophy can be achieved, e.g. by expression of the protein SMN (survival of motor neuron).

For the therapy of a lysosomal storage disease, the expression of glucuronidase, e.g. β-glucuronidase, as a transgene by use of the vectors of the present invention would be promising.

In a further embodiment, the transgene encodes a radioprotective protein such as a radioprotective enzyme. A major limitation of radiotherapy in the treatment of cancer is the radiation-induced damage to the normal tissue, which often makes a reduction in radiation dose, an interruption of the treatment regimen, or even a complete abandonment of this form of therapy necessary. The brain is a particularly radiosensitive organ, which is why primary tumors there often can only be treated to a limited extent with radiotherapy, and diffuse tumor growth usually cannot be treated at all with radiotherapy. With the help of the vectors of the present invention, the healthy tissue surrounding the malignant tissue can be protected by targeted expression of radioprotective proteins. In one preferred embodiment, the transgene which is introduced into the healthy brain tissue is a manganese superoxide dismutase (MnSOD) which catalyzes the conversion of superoxide anions—one of the critical factors in radiation-induced toxicity—to hydrogen peroxide. A further embodiment proposed here involves the kinase domain of the Ataxia telangiectasia mutant (ATM) gene, which contributes to the repair of DNA damage caused by radiation. In a further preferred embodiment, both genes are introduced by means of the presently described vectors into the patient undergoing treatment.

The viral vectors of the present invention are particularly suitable for use in a method of therapeutic treatment of diseases of the brain and/or spinal cord. Diseases of the brain and spinal cord, respectively, in the sense of the present invention comprise genetically caused leukodystrophies, such as adrenoleukodystrophy, Cananvan disease, Krabbe disease, metachromatic leukodystrophy, Pelizaeus-Merzbacher disease and Alexander disease; neurodegenerative diseases such as amyotrophic lateral sclerosis, Alzheimer's disease, Parkinson's disease, Huntington's disease and Pick's disease; chronic-inflammatory diseases of the central nervous system such as Multiple Sclerosis and Guillain-Barré syndrome and lysosomal storage diseases such as ceroid lipofuscinosis and Fabry disease. In a particularly preferred embodiment, the viral vectors of the present invention are for the therapeutic treatment of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease or Huntington's disease.

In yet another embodiment, the transgene encodes an antitumor agent, such as a tumor suppressor protein, or an immunomodulator, such as a cytokine (e.g. interleukin 1 to 4, gamma-interferon, p53), which is intended to be transported selectively to a brain tumor or a tumor of the spinal cord of the patient.

The vectors can also be used to transport antisense-RNA, ribozymes, or the like into cells or tissues of the brain or spinal cord. Furthermore, vectors according to the invention can also comprise transgenes encoding secretory proteins that are intended for being released to the microvasculature of the brain or spinal cord. Such secretory proteins can be effective, e.g. as anti-inflammatory agents.

As used herein, the term “subject” indicates any human or animal organism that can be infected by AAV vectors. Preferably, the subject being treated is a mammal such as a human, a primate, a mouse or a rat. In one preferred embodiment, the subject to be treated is a human. After transfection into the subject, the vector brings about a site-specific expression of the transgene in the cells of the brain or spinal cord.

The transgene can be present in the viral vector in the form of an expression cassette, which in addition to the sequence of the transgene to be expressed comprises further elements necessary for expression, such as a suitable promoter which controls the expression of the transgene after infection of the appropriate cells. Suitable promoters include, in addition to the AAV promoters, e.g. the cytomegalovirus (CMV) promoter or the chicken beta actin/cytomegalovirus hybrid promoter (CAG), an endothelial cell-specific promoter such as the VE-cadherin promoter, as well as steroid promoters and metallothionein promoters. In one particularly preferred embodiment, the promoter used in the vectors according to the invention is a CAG promoter. In one particularly preferred embodiment, the transgene according to the invention comprises a brain-specific promoter which is functionally linked to the transgene to be expressed. In this way, the specificity of the vectors according to the invention for the brain can be further increased. As used herein, a brain-specific promoter is a promoter whose activity in brain tissue is at least 2-fold, 5-fold, 10-fold, 20-fold, 50-fold or 100-fold higher than in a cell which is not a brain cell. Preferably, this promoter is a human promoter. The expression cassette can also include an enhancer element for increasing the expression levels of exogenous protein to be expressed. Furthermore, the expression cassette can include polyadenylation sequences, such as the SV40 polyadenylation sequences or polyadenylation sequences of bovine growth hormone.

The viral vectors according to the invention can, preferably as part of one of their capsid proteins, comprise a peptide sequence of any of SEQ ID NO:1-5. Alternatively, variants of the amino acid sequence of SEQ ID NO:1-5 can be used, the same differing from the amino acid sequence of SEQ ID NO:1-5 by the modification of one amino acid. The modification can be a substitution, deletion or insertion of amino acids, as long as the variant retains the ability to mediate, as part of the capsid, the specific binding of the vector to the receptor structures of cells of the brain and/or spinal cord. The invention therefore also extends to variants of the sequence of SEQ ID NO:1-5 in which the C- or N-terminal amino acid has been changed. These variants have a sequence identity of more than 85% to the amino acid sequence shown in SEQ ID NO:1-5 when the sequences are compared using the programs GAP or BESTFIT. These computer programs for determining amino acid sequence identity are sufficiently known in the art.

The variant of the sequence of SEQ ID NO:1-5 can be based on the substitution of one amino acid—that is, one amino acid can be replaced with another amino acid. Preferably, the substitution by which the variants differ from one of the amino acid sequences in SEQ ID NO:1-5 is a conservative substitution, i.e., a substitution of one amino acid by an amino acid of similar polarity which gives the peptide similar functional properties. Preferably, the substituted amino acid is from the same group of amino acids as the amino acid which is used for the replacement. For example, a hydrophobic residue can be replaced with another hydrophobic residue, or a polar residue by another polar residue. Functionally similar amino acids which can be exchanged for each other by a conservative substitution include, for example, non-polar amino acids such as glycine, valine, alanine, isoleucine, leucine, methionine, proline, phenylalanine, and tryptophan. Examples of uncharged polar amino acids are serine, threonine, glutamine, asparagine, tyrosine, and cysteine. Examples of charged, polar (acidic) amino acids include histidine, arginine and lysine. Examples of charged, polar (basic) amino acids include aspartic acid and glutamic acid.

As variants of the amino acid sequences shown in SEQ ID NO:1-5 are regarded also those amino acid sequences in which an amino acid has been inserted. Such insertions can in principle be carried out as long as the resulting variant retains its ability to bind specifically to cells of the brain or spinal cord. In addition, in the present context, those proteins in which one of the two N-terminal amino acids of SEQ ID NO: 2 is missing are considered to be variants of the amino acid sequence shown in SEQ ID NO:1-5. This requires in turn that the correspondingly deleted variant binds specifically to cells of the brain or spinal cord.

Also encompassed by the invention are specific variants of the amino acid sequences shown SEQ ID NO:1-5 which were structurally modified at one amino acid, for example by introducing a modified amino acid. According to the invention, these modified amino acids can be amino acids that have been modified by biotinylation, phosphorylation, glycosylation, acetylation, branching and/or cyclization.

Viral vectors with capsids that comprise one of the peptide sequences according to the invention, or a variant thereof as defined above, specifically bind to cells of the brain and/or spinal cord. As used herein, a “specific” binding of the vectors according to the invention means that the vectors accumulate after systemic administration mainly on or in the cells of the brain and/or spinal cord. This means that more than 50% of the originally administered vector genomes accumulate in the area of the cells of the brain and/or spinal cord, while less than 50% accumulate in other cells or tissues (such as in the spleen or liver), or in the area thereof. It is preferred that more than 60%, 70%, 80%, 90%, 95%, or even more than 99% of the originally administered vector genomes accumulate in, or in the area of, the cells of the brain and/or spinal cord. Specific binding of the vectors can also be determined via the expression of the transgene. In the case of viral vectors which bind specifically to cells of the brain and/or spinal cord, more than 50% of the total expression of the transgene occurs in, or in the region of, the brain and/or spinal cord, while less than 50% of the expression can be observed in, or in the region of, other tissues. It is preferred, however, that more than 60%, 70%, 80%, 90%, 95%, or even more than 99% of the total measured expression of the transgene occurs in, or in the region of, the brain and/or spinal cord.

A person skilled in the art will easily be able to determine the specific binding of the vectors according to the invention to cells of the brain and/or spinal cord and the expression of the transgene introduced using the vectors. Methods for measuring the specificity of transduction and expression, suitable for this purpose, are shown in the examples below.

It is also preferable according to the invention that vectors whose capsids comprise variants of the amino acid sequences shown in SEQ ID NO:1-5 have at least about 50% of the binding activity of a corresponding viral vector whose capsid has the amino acid sequence shown in SEQ ID NO:1-5. It is even more preferred that the variants have about 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% of the binding activity of a corresponding viral vector whose capsid has the amino acid sequence shown in SEQ ID NO:1-5. The binding activity of the vectors can be measured with the aid of in vitro assays, as described in the included examples.

Preferably, the binding activity of the vectors according to the invention, as can be determined by distribution of the vector genomes or expression of the transgene, for cells of the brain and/or spinal cord is at least 2-fold, 5-fold, 10-fold, 20-fold, 50-fold, 75-fold, 100-fold, 150-fold, 200-fold, 250-fold, 500-fold, 600-fold, 700-fold, 800-fold, 900-fold, 1000-fold, 2000 fold, 5000-fold, or 10,000-fold higher than the binding activity for a control cell which is not a cell of the brain or spinal cord (such as a spleen or liver cell).

The invention also relates to a cell that comprises a peptide, polypeptide or protein according to the invention, a nucleic acid encoding the same, a plasmid comprising such a nucleic acid, or a recombinant AAV vector as described above. It is preferably a human cell or cell line.

In one embodiment, a cell has been, for example, obtained from a human subject by biopsy and then transfected with the viral vector in an ex vivo procedure. The cell can then be re-implanted in the subject, or be supplied in other ways to the subject—for example by transplantation or infusion. The likelihood of rejection of transplanted cells is lower when the subject from which the cell was derived is genetically similar to the subject to which the cell is administered. Preferably, therefore, the subject to whom the transfected cells are supplied is the same subject from which the cells were previously obtained. The cell is preferably a human cell of the brain or spinal cord, particularly a neuronal cell, an endothelial cell of a blood vessel. The cell to be transfected can also be a stem cell, such as a human adult stem cell. It is particularly preferred according to the invention that the cells to be transfected are autologous cells that have been transfected ex vivo with the viral vector according to the invention, for example the recombinant AAV2 vector described above. The cells are preferably used in a method for treating a disorder or disease of the brain and/or spinal cord in a subject.

In another aspect, the invention relates to a method for producing an AAV vector in which a plasmid is used which encodes a capsid protein, the same comprising the amino acid sequence of SEQ ID NO:1 or a variant thereof. Alternatively, the vector can also comprise the amino acid sequence of SEQ ID NO:6, and in particular one of the amino acid sequences of SEQ ID NO:2-5 or a variant thereof. The basic method of producing recombinant AAV vectors comprising a transgene to be expressed is described in the prior art sufficiently [28]. HEK 293-T cells are transfected with three plasmids. A first plasmid comprises the cap and rep regions of the AAV genome, but the naturally occurring inverted repeats (ITRs) are missing. The cap region of this plasmid comprises a gene encoding at least one modified capsid protein, i.e., a gene which comprises the peptide sequence according to the invention. A second plasmid comprises a transgene expression cassette which is flanked by the corresponding ITRs, which constitute the packaging signal. The expression cassette is therefore packaged into the capsid in the course of the assembly of the viral particles. The third plasmid is an adenoviral helper plasmid, on which are encoded the helper proteins E1A, E1B, E2A, E4-orf6, VA, which are required for AAV replication in the HEK 293-T cells. Alternatively, it is also possible to produce the AAV vectors of the present invention in insect cells. A corresponding protocol is provided as an example in the below Example 6.

It was surprisingly found that the production of the recombinant vectors can influence their specificity. In the course of the present invention it was observed that vectors which have been produced in HEK293T cells using the protocol of Example 2 predominantly transfect endothelial cells of the blood vessels of the brain and spinal cord and only to a minor part neurons of the brain or the spinal cord. On the other hand, recombinant vectors which have been produced in Sf-9 cells using the protocol of Example 6 predominantly transfect neurons and to a much smaller extent endothelial cells. This observation can be used for further increasing the specificity of transfection.

Conditions which allow the accumulation and purification of the recombinant vectors according to the invention are known in the art. The vectors according to the invention can be purified, for example, by gel filtration processes—for example using a Sepharose matrix—desalinated, and subsequently purified by filtration. Other purification methods can further comprise a cesium chloride or iodixanol gradient ultracentrifugation process. Purification reduces potentially detrimental effects in the subject to which the adeno-associated viral vectors are administered. The administered virus is substantially free of wild-type and replication-competent virus. The purity of the virus can be checked by suitable methods such as PCR amplification.

In a further aspect, the invention provides a pharmaceutical composition comprising a viral vector of the present invention, particularly an AAV vector. The viral vector in this case is administered in a therapeutically effective amount to the patient, i.e., in an amount sufficient to considerably improve at least one symptom of the dysfunction or disease of the brain and/or spinal cord being treated, or to prevent the progression of the disease. A therapeutically effective amount of the viral vector of the present invention causes a positive change in one of said symptoms, i.e. a change which renders the phenotype of the afflicted subject more similar to the phenotype of a healthy subject that does not suffer from a disease of the brain and/or spinal cord.

In one preferred embodiment according to the invention, the administration of the viral vector occurs in an amount which leads to a complete or substantially complete healing of the dysfunction or disease of the brain and/or spinal cord. The pharmaceutical composition accordingly comprises a therapeutically effective dose of the vector according to the invention. A therapeutically effective dose will generally be non-toxic for the subject who undergoes the treatment.

The exact amount of viral vector which must be administered to achieve a therapeutic effect depends on several parameters. Factors that are relevant to the amount of viral vector to be administered are, for example, the route of administration of the viral vector, the nature and severity of the disease, the disease history of the patient being treated, and the age, weight, height, and health of the patient to be treated. Furthermore, the expression level of the transgene which is required to achieve a therapeutic effect, the immune response of the patient, as well as the stability of the gene product are relevant for the amount to be administered. A therapeutically effective amount of the viral vector can be determined by a person skilled in the art on the basis of general knowledge and the present disclosure.

The viral vector is preferably administered in an amount corresponding to a dose of virus in the range of 1.0×10¹⁰ to 1.0×10¹⁴ vg/kg (virus genomes per kg body weight), although a range of 1.0×10¹¹ to 1.0×10¹³ vg/kg is more preferred, and a range of 5.0×10¹¹ to 5.0×10¹² vg/kg is still more preferred, and a range of 1.0×10¹² to 5.0×10¹² is still more preferred. A virus dose of approximately 2.5×10¹² vg/kg is most preferred. The amount of the viral vector to be administered, such as the AAV2 vector according to the invention, for example, can be adjusted according to the strength of the expression of one or more transgenes.

The viral vector of the present invention, such as the preferred AAV2 vector according to the invention, for example, can be formulated for various routes of administration—for example, for oral administration as a capsule, a liquid or the like. However, it is preferred that the viral vector is administered parenterally, preferably by intravenous injection or intravenous infusion. The administration can be, for example, by intravenous infusion, for example within 60 minutes, within 30 minutes or within 15 minutes. It is further preferred that the viral vector is administered locally by injection to the brain and/or spinal cord during a surgery. Compositions which are suitable for administration by injection and/or infusion typically include solutions and dispersions, and powders from which corresponding solutions and dispersions can be prepared. Such compositions will comprise the viral vector and at least one suitable pharmaceutically acceptable carrier. Suitable pharmaceutically acceptable carriers for intravenous administration include bacteriostatic water, Ringer's solution, physiological saline, phosphate buffered saline (PBS) and Cremophor EL™. Sterile compositions for the injection and/or infusion can be prepared by introducing the viral vector in the required amount into an appropriate carrier, and then sterilizing by filtration. Compositions for administration by injection or infusion should remain stable under storage conditions after their preparation over an extended period of time. The compositions can contain a preservative for this purpose. Suitable preservatives include chlorobutanol, phenol, ascorbic acid and thimerosal. The preparation of corresponding formulations and suitable adjuvants is described, for example, in “Remington: The Science and Practice of Pharmacy,” Lippincott Williams & Wilkins; 21st edition (2005).

In a further aspect, the invention relates to a method for the therapeutic treatment of a disorder or disease of the brain and/or spinal cord, wherein a viral vector according to the invention, preferably an AAV vector as described above, is administered to a subject. The vector comprises a capsid which has at least one capsid protein containing the amino acid sequence of SEQ ID NO:1 or a variant thereof. Alternatively, the vector can also comprise an amino acid sequence of SEQ ID NO:6, in particular an amino acid sequence of SEQ ID NO:2-5 or a variant thereof. The viral vector further comprises a transgene, for example a therapeutic gene, which is useful for the treatment of the disorder or the disease of the brain and/or spinal cord. After administration to the subject being treated, preferably by systemic administration such as intravenous injection or infusion, for example, the vector brings about the specific expression of the gene in the cells of the brain and/or spinal cord.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the in vivo selection method of the AAV-peptide library used according to the invention.

1.: Randomized AAV peptide library with approx. 1×10⁸ different capsid variants;

2.: Withdrawal of the target organ, 8 days after injection;

3.: DNA isolation and amplification of viral DNA fragments via real time PCR;

4.: Cloning into peptide library plasmids for sequencing and production of a secondary peptide library;

5.: Co-transfection of HEK293T cells; production of a secondary peptide library;

6.: secondary AAV peptide library for further rounds of selection; contains pre-selected capsid variants;

7.: intravenous injection of the peptide library into the mouse.

FIG. 2 shows the sequences of the brain-specific peptides identified by means of the selection method. The peptide with the sequence shown in SEQ ID NO:1 was identified in the fourth round of selection.

FIG. 3 shows the gene expression after intravenous injection of recombinant AAV vectors into the living mouse. The luciferase expression was measured 14 days after systemic injection of 5×10¹⁰ vector genomes using the IVIS® 200 Imaging System. A: vectors on the basis of the unmodified AAV2 wild-type capsid show gene expression predominantly in the liver. There is no measurable gene expression in the brain. B: In contrast, the recombinant AAV vector rAAV2-NRGTEWD (SEQ ID NO:1) induces a strong and specific gene expression in the brain.

FIG. 4 shows a long-term expression analysis in mouse after systemic administration of recombinant rAAV2-NRGTEWD (SEQ ID NO:1) vector. Repeated measurements using the IVIS® 200 Imaging System exhibit stable gene expression in the brain over a period of 168 days (n=2).

FIG. 5 shows the results of the determination of luminescence and vector 14 days after intravenous injection of 5×1010 vector genomes of the recombinant AAV vector rAAV2-NRGTEWD (SEQ ID NO:1). A: Measuring gene expression as bioluminescence in the lysates of different organs of the mouse showed a high specificity of the vector for the brain. B: Measuring the distribution of vector genomes in the lysates showed a significant accumulation of the vector in the brain. Mean values+standard deviation. Statistics were calculated by one-way ANOVA. p<0.05=*; p<0.01=**; p<0.001=*** for n=3.

EXAMPLES

All data was determined as mean values+standard deviation (SD). The statistical analysis was performed using the GraphPad Prism 3.0 program (GraphPad Software, San Diego, USA). Data was analyzed by one-way ANOVA followed by multiple comparison tests as per Bonferroni. P values >0.05 were considered significant.

Example 1: Selection of AAV2 Peptide Libraries

For the selection of tissue-specific AAV2 capsids, a random peptide library was prepared and selected in five rounds. A random X₇-AAV peptide library with a theoretical diversity of 1×10⁸ individually occurring clones was prepared using a two-stage protocol as previously described [26-27]. A degenerate oligonucleotide was first produced which codes for seven randomized amino acids at nucleotide position 3967 in the AAV genome, which corresponds to the amino acid position R588 in VP1. The oligonucleotide had the sequence: 5′-CAGTCGGCCAGAGAGGC(NNK)₇GCCCAGGCGGCTGACGAG-3′ (SEQ ID NO:12). The second strand was produced using a Sequenase (Amersham, Freiburg, Germany) and the primer with the sequence 5′-CTCGTCAGCCGCCTGG-3′ (SEQ ID NO:13). The double-stranded insert was cut with BglI, purified with the QIAquick Nucleotide Removal Kit (Qiagen, Hilden, Germany) and ligated into library plasmid pMT187-0-3 that had been digested with SfiI [26]. The diversity of the plasmid library was determined by the number of clones grown from a representative aliquot of transformed, electrocompetent DH5a bacteria on agar containing 150 mg/ml ampicillin. Library plasmids were harvested and purified by using the Plasmid Preparation Kit from Qiagen. The AAV library genomes were packaged into chimeric wild-type and library AAV capsids (AAV transfer shuttle) by transfecting 2×10⁸ 293 T cells in 10 cell culture dishes (15 cm) with the plasmid pVP3 cm (containing the wild-type cap genes with modified codon usage without the inverted terminal repeats) [27], the library plasmids and the pXX6 helper plasmid [28], wherein the ratio between the plasmids was 1:1:2. The resulting AAV library transfer shuttles were used to infect 2×10⁸ 293 T cells in cell culture dishes (15 cm) with an MOI of 0.5 replication units per cell. Cells were superinfected with Ad5 (provided by the Laboratoire de Therapie Génique, France), with an MOI of 5 plaque-forming units (pfu/cell). The final AAV display library was harvested from the supernatants after 48 hours. The supernatants were concentrated using VivaSpin columns (Viva Science, Hannover, Germany) and purified by iodixanol density gradient ultracentrifugation as previously described [29], and titrated by real-time PCR using the cap-specific primers 5′-GCAGTATGGTTCTGTATCTACCAACC-3′ (SEQ ID NO:14) and 5′-GCCTGGAAGAACGCCTTGTGTG-3′ (SEQ ID NO:15) with the LightCycler system (Roche Diagnostics, Mannheim, Germany).

For the in vivo selection 1×10¹¹ particles of the genomic library were injected into the tail vein of FVB/N mice. The particles were given 8 days for the distribution and the infection of the target cells. After 8 days, the mice were killed and the brains were removed. The total DNA of the tissue was extracted using the DNeasy Tissue Kit (Qiagen). The random oligonucleotides that were included in AAV particles of the library and had accumulated in the tissue of interest were amplified by nested PCR using the primers 5′-ATGGCAAGCCACAAGGACGATG-3′ (SEQ ID NO:16) and 5′-CGTGGAGTACTGTGTGATGAAG-3′ (SEQ ID NO:17) for the first PCR and the primers 5′-GGTTCTCATCTTTGGGAAGCAAG-3′ (SEQ ID NO:18) and 5-TGATGAGAATCTGTGGAGGAG-3′ (SEQ ID NO:19) for the second PCR. The PCR-amplified oligonucleotides were used to prepare secondary libraries for three additional rounds of selection. The secondary libraries were generated like the primary libraries (see above), but without the additional step of producing transfer shuttles. The secondary plasmid library was used to transfect 2×10⁸ 293 T cells in cell culture dishes (15 cm) at a ratio of 25 library plasmids per cell, wherein the transfection reagent Polyfect (Qiagen) was used. After each round of selection, several clones were sequenced. The applied selection method is shown in FIG. 1.

Results: After five rounds of selection, several brain-binding capsids were selected. Capsids comprising the peptide sequences NRGTEWD (SEQ ID NO:1) were found to bind particularly strong to cells of the brain and spinal cord (see below). A further group of peptides, which also showed specificity for the brain and spinal cord comprised the peptide ADGVQWT (SEQ ID NO:2), DDGVSWK (SEQ ID NO:3), SDGLTWS (SEQ ID NO:4) and SDGLAWV (SEQ ID NO:5). These peptides comprised the general motif XDGXXWX (SEQ ID NO:6). The peptides obtained in the various rounds of selection are shown in FIG. 2.

Example 2: Preparation and Quantification of Recombinant AAV Vectors in HEK293T Cells

The clones enriched in Example 1 were produced as recombinant AAV vectors and tested for their transduction profile. Recombinant AAV vectors were produced by triple transfection of HEK293T cells. The cells were incubated at 37° C., 5% CO₂ in Dulbecco's modified Eagle Medium (Invitrogen, Carlsbad, USA), supplemented with 1% penicillin/streptomycin and 10% fetal calf serum. Plasmid DNA was transfected into 293T cells with the transfection agent Polyfect (Qiagen, Hilden, Germany). Four days after transfection, the cells were harvested and lysed, and the vectors were purified by means of iodixanol density gradient ultracentrifugation as previously described [29]. For the transfections, pXX6 was used as adenoviral helper plasmid [28], which encodes the luciferase gene pUF2-CMV-luc [27] or the GFP gene pTR-CMV-GFP [30], as was a plasmid encoding the AAV capsid of interest. The plasmids encoding the AAV capsid mutants which had been previously selected from the AAV library, and wild-type controls, were modified pXX2-187 [31] or pXX2 [28]. The inserts were processed as described into library inserts (see above). To quantify the recombinant vectors, the genomic titer was determined by the LightCycler system, as previously described [32], by real-time PCR using the CMV-specific primers 5′-GGCGGAGTTGTTACGACAT-3′ (SEQ ID NO: 20) and 5′-GGGACTTTCCCTACTTGGCA-3′ (SEQ ID NO:21).

Results: It was found that the yield with respect to virus titer for recombinant viruses with luciferase reporter gene was comparable to that of vectors which comprised a wild type AAV2 capsid which indicates that the accumulated peptides do not affect the assembly of the capsid or the packaging of the gene.

Example 3: Examination of the Tropism of the Recombinant AAV Vectors In Vivo

To be able to examine the tropism of the enriched peptides in vivo, the peptides were introduced into the capsid of a recombinant vector comprising a luciferase reporter gene. Vectors with mutated capsids were injected into mice along with control vectors. The AAV vectors were administered intravenously at a dose of 5×10¹⁰ vector genomes (vg)/mouse (n=3 animals per injected AAV clone). On day 14, the animals were anesthetized with isoflurane. The luciferase expression was analyzed using a Xenogen IVIS200 Imaging System (Caliper Lifescience, Hopkinton, USA) with the Living Image 4.0 (Caliper) software, following intraperitoneal injection of 200 μl of luciferin substrate (150 mg/kg, Xenogen) per mouse. Representative, in vivo bioluminescence images of the expression of the transgene at different positions (ventral, dorsal, lateral) were taken when the luminescence in relative light units (photons/sec/cm²) reached the highest intensity.

Then the animals were sacrificed, the organs of interest were removed quickly, and images of the expression of the transgene in individual organs were immediately taken. The organs were then frozen in liquid nitrogen and stored at −80° C. To quantify the luciferase expression, the organs were homogenized in reporter lysis buffer (RLB, Promega, Madison, USA). The determination of the luciferase reporter gene activity was carried out in a luminometer (Mithras LB9 40, Berthold Technologies, Bad Wildbad, Germany) at 10-second intervals after the addition of 100 μL luciferase assay reagent (LAR, Promega), with a 2-second delay between each of the measurements. The values were normalized in each sample with respect to the total amount of protein using the Roti NanoQuant protein assay (Roth, Karlsruhe, Germany).

Results: The in vivo measurement of bioluminescence after 14 days showed that the peptide NRGTEWD (SEQ ID NO:1) led to an expression of the transgene in the brain (10⁴ p/sec/cm²/r). These results were confirmed by the control experiments carried out ex vivo with explanted organs. A randomly selected control clone of the non-selected library (CVGSPCG) (SEQ ID NO:43) led to a weak gene expression that occurred primarily in the heart and in some parts of the abdomen, but not in the brain (not shown). Wild-type AAV2 caused a weak gene expression in the heart, liver and skeletal muscle, but not in the brain (FIG. 3A).

The examination of the luciferase activity of tissue lysates from representative organs revealed that the vectors which comprised the brain-specific NRGTEWD (SEQ ID NO:1) capsid led to a strong and specific gene expression in the brain (1.1×10⁷ RLU/mg protein, see FIG. 5A). In other organ tissues, the NRGTEWD (SEQ ID NO:1) luciferase vector hardly showed expression.

The results further showed that the brain-specific expression of the transgene mediated by the NRGTEWD (SEQ ID NO:1) vector remained organ-specific over a long period. After intravenous administration of the AAV2 NRGTEWD (SEQ ID NO:1) luciferase vectors, the expression of the transgene was measured over a period of 168 days. The radiation emitted in the brain region was determined quantitatively. Over the entire period of time, the expression of the transgene was stable at a high level, and was limited to the brain (FIG. 4).

Example 4: Analysis of the Vector Distribution

In order to check whether the brain-specific expression of the transgene of intravenously injected NRGTEWD (SEQ ID NO:1) vectors is based on a specific homing, first the distribution of vectors was investigated 14 days after intravenous administration of 5×10¹⁰ gp/mouse. The quantification of the vector genomes was performed by real-time PCR. First, the total DNA was extracted from the organ concerned at various time points after intravenous administration of 5×10¹⁰ vg/mouse using a tissue homogenizer (Precellys 24, Peqlab, Erlangen, Germany) and the DNeasy Tissue Kit (Qiagen, Hilden, Germany) according to the manufacturer's instructions. The DNA was quantified using a spectrophotometer (NanoDrop ND-2000C, Peqlab). The analysis of the AAV vector DNA in the tissues was performed by quantitative real-time PCR using the above-described CMV-specific primer, wherein 40 ng of template were used, normalized with respect to the total DNA.

Results: The quantification of the vector genomes by real-time PCR showed a brain-specific homing of NRGTEWD (SEQ ID NO:1). The amount of vector genomes which could be detected in the brain (1.6×10⁴±7.1×10³ vg/100 ng total DNA) was significantly higher than the amount of vector genomes which was detected in another organ (FIG. 5B). To determine the direct correlation between vector homing and expression of the transgene, the vector distribution of wild-type AAV2, the control peptide CVGSPCG and the brain-specific peptide NRGTEWD (SEQ ID NO:1) was measured 14 days after intravenous administration of 5×10¹⁰ gp/mouse, i.e., at the time when the expression of the transgene was determined (see above). The genomes provided by wild-type AAV2 vectors were mainly recovered from the liver and spleen, and the genomes of vectors which had the control peptide were obtained largely from the spleen (data not shown). In total, the amount of vector genomes which were detected in the spleen were relatively equal in all examined capsid variants, suggesting a non-specific capture mechanism for the particles in the reticulo-endothelial system which is independent of the provision and the expression of the transgene. In contrast, the distribution data of genomes which were provided by vectors which had the brain-specific peptide NRGTEWD (SEQ ID NO:1) was highly similar to the expression data of the transgene, with a highly specific accumulation observed in the brain. The amount of vectors detected in the brain which showed the peptide NRGTEWD (SEQ ID NO:1) was about 168-fold higher than in brains, which were injected with a wild-type vector or a control capsid vector. Overall, this data indicates that a brain-specific expression of the transgene, mediated by NRGTEWD (SEQ ID NO:1) vectors, is achieved by a tissue-specific homing of circulating particles.

Example 5: Immunohistochemistry and Histology

Immunohistochemistry was used to visualize the expression of the transgene at the cellular level in the brain, as well as in a control organ, 14 days after the intravenous administration of the rAAV-GFP vector having the peptide NRGTEWD (SEQ ID NO:1) and/or the wild-type AAV capsid as control. The brains of the animals were fixed with 4% (w/v) paraformaldehyde. The tissues were embedded in paraffin. Sections with a thickness of 2 μm were removed from wax, rehydrated and used for immunohistochemistry. An immunohistochemical procedure was performed using polyclonal antibodies for GFP (A-11122, Invitrogen) or CD31 (AB28364, Abcam, Cambridge, USA). The activity of the endogenous peroxidase was inactivated with 1% H₂O₂ in methanol for 30 minutes. Prior to staining with CD31, the sections were heated in citrate buffer (pH 6.0) for 20 minutes at 100° C. After washing in PBS, the sections were incubated for 30 minutes with PBS, 10% goat serum (Vector Lab, Burlingame, USA) and 2% milk powder (Roth). Primary antibodies were allowed to bind for 1 hour at 37° C. After washing in PBS, the sections were incubated for 30 minutes with a secondary, biotinylated goat anti-rabbit antibody (Vector Lab). Bound antibodies were visualized by using the VECTASTAIN-Elite ABC kit (Vector Lab) and 3,3′-diaminobenzidene (DAB, Sigma-Aldrich, St. Louis, USA). Selected sections were counterstained with Hemalum.

Results: In the brains of mice injected with rAAV-NRGTEWD (SEQ ID NO:1), a microscopic examination showed intensive staining of the endothelial cells over the entire microvasculature and to a slightly lesser extent in the large vessels (data not shown). In contrast, brain tissue of mice which was injected with wild-type AAV2 vector showed no staining. To confirm the tissue specificity, the liver was analyzed as a control organ (a tissue which is known to frequently demonstrate high expression of a transgene after injection of wild-type AAV2 vector). In the liver, hepatocyte staining was observed after administration of wild-type rAAV2 vector; but no staining was observed after administration of rAAV2-NRGTEWD (SEQ ID NO:1) vector. The endothelial lineage of cells transduced with the vectors was confirmed by CD31 staining, wherein the pattern obtained by the GFP staining was confirmed in serial sections of the brains of mice injected with rAAV2-NRGTEWD (SEQ ID NO:1) (data not shown).

The examination of the spinal cord of mice which have been injected with rAAV-NRGTEWD (SEQ ID NO:1) also revealed an intensive staining of the endothelial cells of the microvasculature which shows that not only the endothelial cells of the brain but rather the endothelial cells of the complete central nervous system are transducable with the peptides of the invention (data not shown).

Example 6: Production and Quantification of Recombinant AAV Vectors Using the Baculovirus Expression System in Sf9 Insect Cells

For the production of recombinant AAV vectors in Sf9 insect cells [33-35] the modified AAV2 genome having the oligonucleotide insert in the cap gene which encodes the peptide insertion (see above) was cloned into the donor plasmid pFASTBAC Dual (Life Technologies, Darmstadt, Germany). In addition, an artificial intron was inserted into the donor plasmid which included the polh promoter, thereby giving plasmid pFBD-Rep_(in)/Cap_(in) [35]. For establishing the donor plasmid pFB-CAG-eGFP, the CAG promoter and the eGFP gene were cloned together with the SV40 polyadenylation signal and the AAV2 ITRs into plasmid pFASTBAC1 (Life Technologies). The donor plasmids were used for transforming DH10Bac E. coli cells which were subsequently used for isolating recombinant bacmids that comprised the recombinant AAV genome or the eGFP transgene cassette, respectively. The bacmids (9 μg) were used for transfection of 1×10⁶ Sf9 cells using the Fectofly-Transfektionreagenz (Polyplus Transfection/VWR International GmbH, Darmstadt, Germany) in a 6-well format. After 3 days of incubation of the transfected Sf9 insect cells at 27° C. in insect X-Press Medium (Lonza, Cologne, Germany) with 1% Gentamycin (Lonza), 500 μl of the recombinant baculoviruses present in cell culture supernatants were used for the amplification of 2.5×10⁷ fresh Sf9 cells in T175 cell culture flasks for additional 3 days at 27° C. in Insect X-Press Medium (Lonza) with 1% Gentamycin. The baculoviruses amplified in this way were used for infecting fresh Sf9 cells for producing recombinant AAV vectors. For this purpose, recombinant baculovirus with inserted AAV genome and recombinant baculovirus with inserted eGFP transgene cassette were mixed and used together in 400 ml Insect X-Press Medium with 1% Gentamycin in a 1 L Erlenmeyer flask for infecting 6×10⁸ insect cells. The cells were subsequently incubated at 27° C. under agitation (110 rpm). 4 days after infection, the cells were harvested, lysed, and the AAV vectors were purified via iodixanol gradient ultra centrifugation as described before [29]. For quantification of the recombinant vectors, the genomic titer was determined by quantitative real time PCR using the CMV specific primer of SEQ ID NO:20 and SEQ ID NO:21 in the LightCycler system as described before [32].

Results: By using the baculovirus expression system, higher titers of recombinant AAV vectors were achieved in Sf9 insect cells compared to the production in HEK293T cells after triple transfection. While the yield of virus production in HEK293T cells had a maximum of 1.9×10⁴ genomic particles per cell, a yield of up to 7.9×10⁴ genomic particles per cell were observed in Sf9 insect cells. It could further be observed that rAAV2-NRGTEWD (SEQ ID NO:1) vectors produced in Sf9 insect cells had a higher affinity for neurons than comparable recombinant vectors, which have been produced in HEK293T cells (data not shown). Thus, the choice of the specific production process for the recombinant vectors provides the possibility of increasing the specificity of the vectors for the neuron or endothelial cells, respectively.

READINGS

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1. A peptide, polypeptide, or protein that specifically binds to cells of the brain and/or spinal cord, characterized in that it comprises the amino acid sequence of SEQ ID NO:6.
 2. A peptide, polypeptide, or protein according to claim 1, characterized in that it comprises the following: (a) one of the amino acid sequences of SEQ ID NO:2-5, or (b) an amino acid sequence which differs from the amino acid sequence of SEQ ID NO:1 by modification of one amino acid.
 3. The protein according to claim 1, which is a capsid protein of a viral vector, preferably a capsid protein of an adeno-associated virus (AAV).
 4. The protein according to claim 3, which is a capsid protein of an AAV of a serotype selected from the group consisting of serotypes 2, 4, 6, 8, and
 9. 5. The protein according to claim 4, which is a capsid protein of an AAV of serotype
 2. 6. (canceled)
 7. The protein according to claim 1, wherein the peptide is present in the region of amino acids 550-600 of the capsid.
 8. The protein according to claim 1, comprising the following: (a) an amino acid sequence having at least 80% identity to the amino acid sequence of SEQ ID NO:10 and further comprises the sequence of SEQ ID NO:1 or an amino acid sequence which differs from the amino acid sequence of SEQ ID NO:1 by modification of one amino acid; or (b) a fragment of the amino acid sequences defined in (a).
 9. A viral capsid which comprises a peptide, polypeptide, or protein according to claim
 1. 10. A nucleic acid which encodes a peptide, polypeptide, or protein comprising the amino acid sequence of SEQ ID NO:6 that specifically binds to cells of the brain and/or spinal cord.
 11. A plasmid which comprises a nucleic acid according to claim
 10. 12. A recombinant viral vector which comprises a capsid and a transgene packaged therein, wherein the capsid comprises at least one capsid protein comprising a peptide, polypeptide, or protein comprising the amino acid sequence of SEQ ID NO:6 that specifically binds to cells of the brain and/or spinal cord.
 13. The recombinant viral vector according to claim 12, which is a recombinant AAV vector.
 14. The recombinant viral vector according to claim 13, which is an AAV vector of a serotype selected from the group consisting of serotypes 2, 4, 6, 8, and
 9. 15. (canceled)
 16. The recombinant viral vector according to claim 12, wherein the transgene encodes one of the following proteins: a membrane or tight junction protein, a neuraminidase, glucuronidase, a chemokine antagonist, neurotrophic factor of glia cells (GDNF), neprilysine, cholesterol 24 hydroxylase, aromatic L-amino acid decarboxylase, a tyrosine hydroxylase, GTP cyclohydrolase I, and survival of motor neuron (SMN) protein.
 17. The recombinant viral vector according to claim 16, wherein the transgene encodes a neuraminidase.
 18. The recombinant viral vector according to claim 12, wherein the transgene is in the form of an ssDNA or a dsDNA.
 19. A method for the targeted delivery of viral vectors to the brain and/or spinal cord in a subject, comprising administering a recombinant viral vector according to claim 12 to the subject.
 20. The method of claim 19, wherein the vector is formulated for intravenous administration.
 21. A cell which comprises a peptide, polypeptide, or protein according to claim
 1. 22. A pharmaceutical composition which comprises a peptide, polypeptide, or protein according to claim
 1. 